The use of a single breaker plate in spin packs is known. Also, the use of various filtering media in spin packs is known; filtering media such as sand, cintered metal, and wire mesh screens have been proposed and used.
When extruding non-pigmented, or natural, synthetic yarn, the life of the spin pack depends to a certain extent of the effectiveness of the filtering media. Spin packs normally have to be changed when either the pressure of the melt in the pack becomes too high due to the filtering media clogging, or when the distribution at the spinnerette has deteriorated so that too many yarns are outside the denier specification being used. Sometimes a pack seal leaks and causes the spin pack to be changed. More occasionally, a spin pack has to be changed because one or more capillaries becomes blocked or partially blocked. Pack changing necessitates interrupting extrusion, and apart from the down time involved, causes substantial waste as the spin system is "threaded-up" again.
The problems of down time and waste associated with melt spinning solution dyed yarns or filaments, such as solution dyed polypropylene, are far more severe. In addition to the problems mentioned above with natural yarns, two further problems exist; namely, the additional clogging of the filtering media by the color pigments, some of which clog more readily than others, and the necessity to change color. Color changing is frequently accompanied by a pack change, and also with a long purge without packs to clean out from the spin system traces of the previous color before putting in new packs and introducing the new color. This becomes very costly if only a short run of a particular color is required, for example, 5000 pounds or less, and even more so if 1,000 pounds or less is required.
Another problem that occurs sometimes is that a spin pack is incorrectly or poorly assembled. This is not discovered until the extrusion line is brought up and the pack malfunctions. The line then has to be brought down again and the faulty pack changed causing more down time and waste. Some causes of this are incorrectly positioned seals and incorrectly located filtering media.